1. Field of the Invention
The present invention relates to an image formation apparatus which can detect a stack of sheets on a tray.
2. Related Background Art
Conventionally, it has been known that a sorter is attached to a copy machine to sort copied sheets.
In addition to such a function for sorting the discharged sheets, the sorter can also have a function for executing a processing to staple the sheets stacked on each tray (to be referred as staple processing hereinafter).
Recently, since a facsimile function and a printer function have been added to the copy machine, the sorter is used not only as a copied-sheet discharging destination but also as sheet outputting destinations of a printer, a facsimile and a filing apparatus.
In any case, when the printing is intended to be executed by using the conventional sorter, if the sheets remain on the tray, it is interrupted to execute the printing until the remaining sheets are removed, in order to prevent that, when the copied or printed sheets are subjected to the staple processing, the sheets for which the staple processing is necessary and the other sheets are mixed and then subjected to the staple processing.
However, when the sorter is used in the printer, even if images and text formed based on plural application softwares together construct one volume, the printing processing is not executed if the sheets are not removed from the sorter every time the printing based on each application software terminates. Therefore, such the printing can not be effectively utilized.